COMPONENTS OF PENSION AND OTHER POST-EMPLOYMENT BENEFIT (OPEB) PLANS NET PERIODIC BENEFIT COSTS - Schedule of Components of Net Periodic Benefit (Credit) Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 987	$ 288	$ 2,963	$ 863
Interest Cost	6,275	5,876	18,825	17,628
Expected Return on Plan Assets	(10,114)	(10,092)	(30,343)	(30,277)
Amortization of Prior Service Credits	(92)	(126)	(275)	(377)
Amortization of Actuarial Loss	1,490	2,179	4,469	6,537
Net Periodic Benefit (Credit) Cost	(1,454)	(1,875)	(4,361)	(5,626)
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0	0	0
Interest Cost	4,580	4,677	13,740	14,030
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credits	(601)	(601)	(1,804)	(1,804)
Amortization of Actuarial Loss	2,315	4,051	6,946	12,154
Net Periodic Benefit (Credit) Cost	$ 6,294	$ 8,127	$ 18,882	$ 24,380